A differential capacitive sensor and a connecting column forming method thereof

Abstract

The present invention relates to a differential capacitive sensor and a method for forming a connecting column thereof, wherein the sensor comprises: a back plate; a first diaphragm and a second diaphragm located on both sides of the back plate, the first diaphragm and the second diaphragm are respectively spaced apart from the back plate, the edges of the first diaphragm and the second diaphragm are sealed and connected, a low-pressure sealed cavity is formed between the first diaphragm and the second diaphragm, and the back plate is located in the low-pressure sealed cavity; a plurality of connecting columns, the connecting columns pass through the back plate and connect the first diaphragm and the second diaphragm, the plurality of connecting columns are spaced apart and distributed in the plane of the back plate, a through hole for the connecting columns to pass through is provided on the back plate, the connecting columns comprise a connecting block and a hollow connecting tube, one end of the connecting tube is connected to the first diaphragm, and the other end passes through the back plate and is connected to the second diaphragm through the connecting block. The present application can improve the stress condition of the diaphragm at the connecting column and the stress condition of the connecting column itself, thereby improving the reliability of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a differential capacitive sensor and a method for forming a connecting column thereof. Background Art

[0002] like Figure 1 As shown in the figure, the MEMS microphone consists of three parts: MEMS Sensor (MEMS chip), ASIC chip (interface circuit dedicated chip) and package. The performance of MEMS microphone is mainly determined by the MEMS chip. Usually, the MEMS chip mainly includes three parts: diaphragm, back plate and substrate. The back plate has through holes. The diaphragm and the back plate constitute a flat capacitor. A bias voltage is applied to the diaphragm or the back plate. The sound pressure acts on the diaphragm, causing the distance between the diaphragm and the back plate to change, thereby causing the capacitance to change and generating a voltage signal output.

[0003] For traditional MEMS chips with a single-layer diaphragm structure, since there is an air gap between the diaphragm and the back plate, the air gap between the diaphragm and the back plate will produce film damping, resulting in a large background noise in the microphone. To solve this problem, the patent with publication number CN118158603A discloses a MEMS chip with a double-layer diaphragm structure, which is provided with a diaphragm on both sides of the back plate, and the edges of the two diaphragms are sealed to form a low-pressure sealed cavity between the two diaphragms, thereby reducing the air film damping between the diaphragm and the back plate and reducing the background noise. At the same time, the two diaphragms are connected by connecting columns to achieve mechanical coupling, so that the two diaphragms vibrate synchronously to achieve the output of differential signals and offset the interference of noise signals.

[0004] For the MEMS chip with the above-mentioned double-layer diaphragm structure, a pressure difference is formed between the low-pressure area between the double-layer diaphragms and the ambient atmospheric pressure. The diaphragm is subjected to a pressure close to the ambient atmospheric pressure. Under the action of this force, there is great stress at the contact point between the diaphragm and the connecting column and at the connecting column itself, which makes the device prone to the risk of structural damage. Summary of the invention

[0005] Based on the above description, the present invention provides a differential capacitive sensor and a method for forming a connecting column thereof to solve the problem that there is a large stress at the contact position between the diaphragm and the connecting column and at the connecting column itself, and the device is prone to the risk of structural damage.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] In a first aspect, the present application provides a differential capacitive sensor, and the technical solution adopted is as follows:

[0008] A differential capacitive sensor, comprising:

[0009] Back panel;

[0010] A first diaphragm and a second diaphragm are respectively located on both sides of the back plate, the first diaphragm and the second diaphragm are respectively spaced apart from the back plate, the edges of the first diaphragm and the second diaphragm are sealed and connected, a low-pressure sealed cavity is formed between the first diaphragm and the second diaphragm, and the back plate is located in the low-pressure sealed cavity;

[0011] Multiple connecting columns, the connecting columns pass through the back plate and connect the first diaphragm and the second diaphragm, the multiple connecting columns are spaced apart in the plane of the back plate, and a through hole is provided on the back plate for the connecting columns to pass through. The connecting columns include a connecting block and a hollow connecting tube, one end of the connecting tube is connected to the first diaphragm, and the other end passes through the back plate and is connected to the second diaphragm through the connecting block.

[0012] Preferably, the connecting column further comprises a core filled in the connecting tube.

[0013] Preferably, the dielectric constant of the core material is smaller than the dielectric constant of the connecting tube material.

[0014] Preferably, the connecting pipe and the connecting block are integrally formed.

[0015] Preferably, the core material and the connecting tube material have an etching selectivity ratio.

[0016] Preferably, the projection of the connecting block on the second diaphragm covers the projection of the connecting tube on the second diaphragm.

[0017] In a second aspect, the present application provides a method for forming a connection column of a differential capacitive sensor, which is used to form the connection column of the differential capacitive sensor as described above, comprising:

[0018] Depositing a first material on the first diaphragm to form a sacrificial layer;

[0019] An annular groove is etched in the sacrificial layer, and a core is formed inside the annular groove;

[0020] Depositing a second material having an etching selectivity ratio with the first material on the sacrificial layer to fill the annular groove, the deposited second material forming a portion covering the sacrificial layer and a portion filling the annular groove, the portion of the second material filling the annular groove forming a connecting pipe;

[0021] Etching and removing the non-connecting block portion of the portion of the second material covering the sacrificial layer to form a connecting column including a core body. If the designed connecting column structure includes a core body, the desired connecting column is obtained. If the designed connecting column structure does not include a core body, the following steps are further included:

[0022] Continue etching to remove the core to form a connection column excluding the core, thereby obtaining the desired connection column.

[0023] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0024] 1. The present application configures a connecting column connecting the first diaphragm and the second diaphragm to include a connecting tube and a connecting block. The connecting tube can increase the cross-sectional size of the connecting column, increase the structural strength of the connecting column, and increase the connection area between the connecting column and the first diaphragm. At the same time, the connecting block increases the connection area between the connecting column and the second diaphragm, that is, increases the force-bearing area of ​​the connection between the diaphragm and the connecting column, thereby reducing the stress at the connection between the diaphragm and the connecting column, improving the stress condition of the diaphragm at the connecting column and the stress condition of the connecting column itself, reducing the risk of structural damage to the diaphragm and the connecting column, and improving the reliability of the device.

[0025] 2. The differential capacitive sensor of the present application is provided with a core body in the connecting tube, and the core body can further enhance the structural strength of the connecting column.

[0026] 3. The connecting column forming method of the present application is to first etch a reserved annular groove for a connecting tube in a sacrificial layer formed by depositing a first material, form a core body on the inner side of the annular groove, and then deposit a second material to fill the annular groove to form a connecting tube. Finally, the non-connecting block portion is etched away to obtain a connecting column including the core body. The thickness of the deposited second material only needs to reach 1 / 2 of the width of the annular groove, and the thickness of the annular groove depends on the wall thickness of the connecting tube. The wall thickness of the connecting tube is less than the overall diameter of the connecting column, that is, the thickness of the deposited second material is smaller, and the step height formed after etching away the non-connecting block portion is lower. When the second diaphragm is subsequently deposited, the step height formed on the second diaphragm is low, which has little effect on the stiffness of the second diaphragm. The molding process steps are the same as the traditional process steps, and only the shape of the filling hole etched in the sacrificial layer needs to be changed, thereby avoiding the complication of the process.

[0027] 4. The present application designs the connecting column structure and the molding process. On the premise of increasing the cross-sectional size of the connecting column and improving the contact position between the diaphragm and the connecting column and the stress condition of the connecting column itself, the molding process of the connecting column is simple, which can ensure the stiffness of the diaphragm while avoiding the complication of the process and the increase of parasitic capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The accompanying drawings are background technology of the present invention;

[0029] Figure 2 A schematic diagram of a method for completely filling a filling hole by depositing a connecting column material in the related art;

[0030] Figure 3 A schematic diagram of a method for incompletely filling a filling hole by depositing a connecting column material in the related art;

[0031] Figure 4 A schematic structural diagram of a differential capacitive sensor provided by an embodiment of the present invention, wherein the connecting column includes a core body;

[0032] Figure 5 A schematic diagram of the structure of a differential capacitive sensor provided by an embodiment of the present invention, wherein the connecting column does not include a core;

[0033] Figure 6 A schematic diagram of step 1 in a method for forming a connection column of a differential capacitive sensor provided in an embodiment of the present invention;

[0034] Figure 7 A schematic diagram of step 2 in the method for forming a connection column of a differential capacitive sensor provided in an embodiment of the present invention;

[0035] Figure 8 A schematic diagram of step 3 in the method for forming a connection column of a differential capacitive sensor provided in an embodiment of the present invention;

[0036] Fig. 9 A schematic diagram of step 4 in the method for forming a connection column of a differential capacitive sensor provided in an embodiment of the present invention;

[0037] Fig.10 A schematic diagram of step 5 in the method for forming a connection column of a differential capacitive sensor provided in an embodiment of the present invention.

[0038] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0039] 1. Back plate; 2. First diaphragm; 3. Second diaphragm; 31. Release hole; 4. Connecting column; 41. Connecting tube; 42. Connecting block; 43. Core body. DETAILED DESCRIPTION

[0040] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] It will be appreciated that spatial relationship terms such as "under," "beneath," "below," "under," "above," "above," etc., may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It will be appreciated that, in addition to the orientations shown in the figures, spatial relationship terms also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, an element or feature described as "under other elements" or "under it" or "under it" will be oriented as being "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0043] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element, or connected to the other element through an intermediate element. The "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0044] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0045] At present, for MEMS chips with a double-layer diaphragm structure, the method for forming the connecting columns is generally to first deposit a sacrificial layer on the deposited lower diaphragm, then etch reserved filling holes for the connecting columns in the sacrificial layer, and then deposit connecting column material on the sacrificial layer to fill the filling holes to form connecting columns. After the connecting columns are formed, the connecting column material of the non-connecting column part is etched away, so that when the upper diaphragm is subsequently deposited, the diaphragm only contains the silicon electrode layer, thereby having a smaller diaphragm stiffness.

[0046] Regarding the problem that there is great stress at the contact point between the diaphragm and the connecting column and at the connecting column itself, which leads to the risk of structural damage to the device, the traditional solution is to directly increase the diameter of the connecting column to increase the force-bearing area at the connection between the diaphragm and the connecting column, thereby achieving the purpose of improving the contact point between the diaphragm and the connecting column and the stress situation of the connecting column itself.

[0047] For connecting posts with larger cross-sectional dimensions, there are two filling methods for depositing connecting post material to fill the filling holes during molding, such as Figure 2 As shown in the figure, one method is to completely fill the filling hole, then the thickness of the deposited connecting column material is at least 1 / 2 of the filling hole diameter. After the subsequent etching to remove the connecting column material of the non-connecting column part, a large step will be formed. When the upper diaphragm is deposited later, it will cause a large step on the upper diaphragm, thereby affecting the stiffness of the upper diaphragm. To solve this problem, the connecting column material needs to be etched and thinned before depositing the upper diaphragm, which will complicate the process. Figure 3 As shown in FIG. 1 , another method is to incompletely fill the filling hole. This method can reduce the thickness of the deposited connection column material, but when the upper diaphragm is subsequently deposited, the upper diaphragm material will fill into the filling hole, causing the distance between the two diaphragm electrodes to become closer, increasing the parasitic capacitance. Both filling methods have defects.

[0048] Reference Figure 4-5 As shown, in order to solve the above problems, an embodiment of the present application provides a differential capacitive sensor, which includes a back plate 1, a first diaphragm 2, a second diaphragm 3 and a plurality of connecting posts 4, wherein the first diaphragm 2 and the second diaphragm 3 are respectively located on both sides of the back plate 1, the first diaphragm 2 and the second diaphragm 3 are respectively spaced apart from the back plate 1, the edges of the first diaphragm 2 and the second diaphragm 3 are sealed and connected, a low-pressure sealed cavity is formed between the first diaphragm 2 and the second diaphragm 3, the back plate 1 is located in the low-pressure sealed cavity, the connecting posts 4 pass through the back plate 1 and connect the first diaphragm 2 and the second diaphragm 3, a plurality of connecting posts 4 are spaced apart in the plane of the back plate 1, and a through hole for the connecting posts 4 to pass through is provided on the back plate 1. Among them, the connecting posts 4 include a connecting block 42 and a hollow connecting tube 41, one end of the connecting tube 41 is connected to the first diaphragm 2, and the other end passes through the back plate 1 and is connected to the second diaphragm 3 through the connecting block 42.

[0049] Reference Figure 4-5 As shown, further, the connecting column 4 may also include a core 43 filled in the connecting tube 41, and the core 43 fills the cavity in the connecting tube 41 to form a solid connecting column 4 structure, which can further improve the structural strength of the connecting column 4. Whether to include the core 43 is selected according to needs in actual design.

[0050] Furthermore, the dielectric constant of the core 43 material is smaller than that of the connecting tube 41 material, which can reduce the parasitic capacitance between the two diaphragms compared to the connecting column 4 formed entirely of the connecting tube 41 material. At the same time, the core 43 material and the connecting tube 41 material have an etching selectivity ratio, so that when the connecting column 4 does not need the core 43, the core 43 can be etched away alone.

[0051] Furthermore, the connecting tube 41 and the connecting block 42 are integrally formed, that is, the connecting tube 41 and the connecting block 42 are made of the same material, so that the connecting tube 41 and the connecting block 42 can be deposited and formed simultaneously during molding, simplifying the process and making the connecting block 42 and the connecting tube 41 have a higher connection strength. The projection of the connecting block 42 on the second diaphragm 3 covers the projection of the connecting tube 41 on the second diaphragm 3, and the connecting column 4 is connected to the second diaphragm 3 through the connecting block 42. The connection area between the connecting block 42 and the second diaphragm 3 is larger, and the force-bearing area of ​​the diaphragm is larger, further reducing stress.

[0052] Specifically, the cross-sectional shape of the connecting tube 41 can be a circular ring, an elliptical ring or a polygonal ring, the cross-sectional shape of the corresponding core 43 is the same as the inner circular shape of the cross-sectional shape of the connecting tube 41, and the cross-sectional shape of the connecting block 42 is designed to be the same as the outer circular shape of the cross-sectional shape of the connecting tube 41. The strength of the connecting column 4 is made uniform, and the connection between the first diaphragm 2 and the second diaphragm 3 and the connecting column 4 is uniformly stressed around to avoid stress concentration.

[0053] Reference Figure 6-10 As shown, this embodiment also provides a method for forming a connection column of the differential capacitive sensor, comprising the following steps:

[0054] Step 1: Deposit a first material on the first diaphragm 2 to form a sacrificial layer. Figure 6 As shown, the thickness of the sacrificial layer is the length of the connecting tube 41, and the material can be SiO2.

[0055] Step 2: Etch an annular groove in the sacrificial layer, and form a core 43 inside the annular groove. Figure 7 As shown, the annular groove is a reserved filling hole for the connecting pipe 41 , which is subsequently filled with the connecting pipe 41 material to form the connecting pipe 41 .

[0056] Step 3: Deposit a second material having an etching selectivity ratio with the first material on the sacrificial layer to fill the annular groove. The deposited second material forms a portion covering the sacrificial layer and a portion filling the annular groove. The portion of the second material filling the annular groove forms a connecting tube 41. Figure 8 As shown, the second material can be SiN or polysilicon, which has an etching selectivity ratio with the first material to facilitate subsequent etching to remove the sacrificial layer. The thickness of the deposited second material needs to exceed 1 / 2 of the width of the annular groove to ensure that the annular groove is completely filled.

[0057] Step 4: Etch and remove the non-connecting block 42 portion of the second material covering the sacrificial layer to form a connecting column 4 including a core 43. Fig. 9As shown, the portion of the second material covering the sacrificial layer needs to be etched away in the non-connecting block 42 portion, so that when the second diaphragm 3 of the upper layer is subsequently deposited, the second diaphragm 3 does not include the second material to reduce the stiffness of the second diaphragm 3. After this step, the connecting column 4 with the core 43 is obtained. If the designed connecting column 4 includes the core 43, the required connecting column 4 is obtained after this step. If the designed connecting column 4 structure does not include the core 43, the following steps are also included:

[0058] Step 5: Continue etching to remove the core 43, forming a connecting column 4 excluding the core 43, and obtaining the desired connecting column 4, such as Fig.10 Specifically, after the upper second diaphragm 3 is deposited and formed, a release hole 31 is etched on the upper second diaphragm 3 at the position of the connecting column 4, and the core 43 of the connecting column 4 is further etched away, and the core 43 material is released through the release hole 31.

[0059] Compared with the traditional forming method of the connecting column 4, the etching of the annular groove in the sacrificial layer in the present application will not cause any complication in the process. In addition, the deposition thickness of the second material in the present application only needs to reach 1 / 2 of the width of the annular groove, and the thickness of the annular groove depends on the wall thickness of the connecting tube 41. The wall thickness of the connecting tube 41 is less than the overall diameter of the connecting column 4, that is, the thickness of the deposited second material is small, and the step height formed after etching away the non-connecting block 42 is low. When the second diaphragm 3 is subsequently deposited, the step height formed on the second diaphragm 3 is low, and the stiffness of the second diaphragm 3 is little affected. That is, the connecting column 4 structure and forming method of the present application, under the premise of improving the contact position between the diaphragm and the connecting column 4 and the stress condition of the connecting column 4 itself, the forming process of the connecting column 4 is simple, which can ensure the stiffness of the diaphragm while avoiding the complication of the process and the increase of parasitic capacitance.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A differential capacitive sensor, characterized in that: include: Back panel (1); A first diaphragm (2) and a second diaphragm (3) are respectively located on both sides of the back plate (1); the first diaphragm (2) and the second diaphragm (3) are respectively spaced apart from the back plate (1); the edges of the first diaphragm (2) and the second diaphragm (3) are sealed and connected; a low-pressure sealed cavity is formed between the first diaphragm (2) and the second diaphragm (3); and the back plate (1) is located in the low-pressure sealed cavity; a plurality of connecting posts (4), the connecting posts (4) passing through the back plate (1) and connecting the first diaphragm (2) and the second diaphragm (3); the plurality of connecting posts (4) are spaced apart in the plane of the back plate (1); a through hole for the connecting posts (4) to pass through is provided on the back plate (1); the connecting posts (4) comprise a connecting block (42) and a hollow connecting tube (41); one end of the connecting tube (41) is connected to the first diaphragm (2), and the other end passes through the back plate (1) and is connected to the second diaphragm (3) via the connecting block (42); The connecting column (4) further comprises a core (43) filled in the connecting tube (41); The forming method of the connecting column (4) comprises: Depositing a first material on the first diaphragm (2) to form a sacrificial layer; Etching an annular groove in the sacrificial layer, forming a core (43) inside the annular groove; Depositing a second material having an etching selectivity ratio with the first material on the sacrificial layer to fill the annular groove, the deposited second material forming a portion covering the sacrificial layer and a portion filling the annular groove, the portion of the second material filling the annular groove forming a connecting tube (41); The non-connecting block (42) part of the second material covering the sacrificial layer is removed by etching to form a connecting column (4) including a core (43). If the designed connecting column (4) structure includes the core (43), the desired connecting column (4) is obtained. If the designed connecting column (4) structure does not include the core (43), the connecting column (4) is further comprised of: Continue etching to remove the core (43) to form a connection column (4) that does not include the core (43), thereby obtaining the desired connection column (4).

2. The differential capacitive sensor according to claim 1, characterized in that: The dielectric constant of the material of the core (43) is smaller than the dielectric constant of the material of the connecting tube (41).

3. The differential capacitive sensor according to claim 1, characterized in that: The core (43) material and the connecting tube (41) material have an etching selectivity ratio.

4. The differential capacitive sensor according to claim 1, characterized in that: The connecting pipe (41) and the connecting block (42) are integrally formed.

5. The differential capacitive sensor according to claim 1, characterized in that: The projection of the connecting block (42) on the second diaphragm (3) covers the projection of the connecting tube (41) on the second diaphragm (3).

6. A method for forming a connection column of a differential capacitive sensor, used for forming the connection column (4) of the differential capacitive sensor according to claim 1, characterized in that: include: Depositing a first material on the first diaphragm (2) to form a sacrificial layer; Etching an annular groove in the sacrificial layer, forming a core (43) inside the annular groove; Depositing a second material having an etching selectivity ratio with the first material on the sacrificial layer to fill the annular groove, the deposited second material forming a portion covering the sacrificial layer and a portion filling the annular groove, the portion of the second material filling the annular groove forming a connecting tube (41); The non-connecting block (42) part of the second material covering the sacrificial layer is removed by etching to form a connecting column (4) including a core (43). If the designed connecting column (4) structure includes the core (43), the desired connecting column (4) is obtained. If the designed connecting column (4) structure does not include the core (43), the connecting column (4) is further comprised of: Continue etching to remove the core (43) to form a connection column (4) that does not include the core (43), thereby obtaining the desired connection column (4).

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